1. HE’S ADORABLE

Out of all the talent picked up by Apatow’s comedy machine, Rudd is by far the handsomest. He was in a Perry Ellis ad, for God’s sake! Jonah Hill has his wide-eyed disbelief, Jason Segel has that tender gaze that threatens to turn creepy at any moment (see “Knocked Up”) and Seth Rogen lights up the screen with his bearish grin, but there’s something disarming about Rudd’s wry little half-smile that can make even the most steadfastly unemotional bro melt in his seat. I mean, did you see him in “Clueless”? Did you SEE him?

2. “YOU KNOW HOW I KNOW YOU’RE GAY?”

Who can forget the pivotal moment in Apatow’s big screen debut, “The 40 Year Old Virgin,” in which David (Rudd) discloses to Cal (Rogen) the telltale signs of being a homosexual male: macraméing yourself a pair of jean shorts and listening to Coldplay. Rudd’s perfect delivery has served as a template for straight guys to use in order to emasculate one another ever since. Rudd’s character in the movie also codified for the first time the role of the bromantic that has served him so well since. His consciousness of his own sensitivity and acknowledgement of the quasi-homosexual nature of platonic male-male friendships set the standard: other members of the group have since riffed on it to create their own individualized permutations (Segel in “Forgetting Sarah Marshall,” anyone?).

3. HE’S SURPRISINGLY OLD

You may not have noticed, but Rudd casually turned 40 on Monday, making him the oldest member of the Apatow crew short of the big daddy himself (he’s 41). So what’s he doing hanging out with a bunch of 20-somethings? They need him! Can you imagine Segel in Rudd’s role in “I Love You, Man”? Rudd offers a mature counterbalance to the group’s humor, often providing the foil necessary for the films’ driving characters. In “Virgin” he’s the relationship man; in “Knocked Up” he’s the husband who hilariously sketches out for us the troubles of marital life (“Marriage is like a tense, unfunny version of ‘Everybody Loves Raymond,’ only … it lasts forever,” he tells Rogen). You can’t have the type of development on which these bromances thrive without the guy who’s been there, and that guy is almost always Rudd.

4. HE KNOWS WHO HE IS (AND WHO HE AIN’T)

Rudd knows his limits and how to utilize his niche to the fullest extent. He has been typecast within the Apatow gang to this end, but Rudd’s true talent as an actor lies in his ability to nuance each performance to create recognizably distinct characters despite the fact that they often face similar situations. The sweet, hopelessly awkward Peter Klaven (“I Love You, Man”) is definitively not the caustic, emotionally handicapped Pete of “Knocked Up,” but Rudd fits both roles like a glove. He reinvents and inhabits the minds of decent guys fraught with bourgeois angst in each role he plays (except his minor role as Chuck in “Forgetting Sarah Marshall,” in which he kind of sucked but we’ll forgive him). But as he exhibited in his screenwriting debut, “Role Models,” he is also able to create the worlds around those characters.

5. HE IS YOU, AND IF HE’S NOT, HE’S SOMEONE YOU KNOW

Rudd plays regular Joes in a way that trumps both his predecessors and his contemporaries. Out of the usual suspects, Segel is too girly, Rogen is too arrogant (and in my opinion also not that great of an actor), and Hill is too high-strung to be truly relatable. In “I Love You, Man,” Rudd is awkward, decent, well-meaning and struggling with his relationships not with women but with men. If the new successful American comedy standard is the male self-conscious of his own self-consciousness, then Rudd is surely its hero.